Many mobile or portable electronic devices, such as cellular telephones, portable computers, cameras, and camcorders operate on battery power. Thus, reducing power consumption is an important issue, as consumers increasingly demand longer times between recharging.
One known method for minimizing power consumption in electronic devices is to place the device in a low-power standby mode, as compared to an active mode, in which power to all unnecessary circuitry is reduced or removed while the device is idle. Generally, power consumption is further minimized by monitoring or measuring power consumption and controlling or adjusting power supplied to circuits and elements in the device using a power measurement circuit. Typically, the power measurement circuit includes separate circuits for measuring both power consumption in the active mode, and power consumption in the standby mode, commonly referred to as leakage current.
One circuit or element commonly powered down when a battery operated device is idle is a semiconductor memory. A memory typically includes a memory core with from one million to a few million or more cells, each having one or more active elements, transistors, which may be programmed to store data. A conventional power measurement circuit 100 for measuring and controlling power consumption in a memory core 102 in standby mode is shown in FIG. 1. Referring to FIG. 1, the power measurement circuit 100 typically includes a leakage measurement circuit 104 having a baseline element or device 106 coupled in series with a reference current source 108 between a supply voltage (Vcch) and electrical ground (Vgnd). The supply voltage supplies power to the memory core 102. The baseline device 106 is a scaled replica of the memory core 102 so that leakage current through the memory core in standby mode can determined or approximated by measuring current through the baseline device. That is the baseline device a replica of the entire million cell core representative of millions of cells. The power measurement circuit 100 further includes a comparator 110 and body biasing control circuitry, such as a negative charge pump 112, coupled between an output of the comparator and body or bulk contacts of active elements (not shown) in the memory core 102. In operation, the voltage (ml) dropped by the baseline device 106, which is dependent on leakage current therethrough, is compared with a predetermined, known reference voltage (VBG). If the baseline device 106 leakage is higher than predetermined value, the comparator 110 triggers or enables the negative charge pump 112, and a reverse body bias is applied to memory cell transistors as well as to the baseline device 106, thereby reducing leakage current through the memory core 102.
Power consumption in the active mode or active current for the memory chip can be measured and controlled using a separate power measurement circuit (not shown). In one conventional or known method, described for example in Rich McGowen, “Power and Temperature Control on a 90-nm Itanium Family Processor” IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 41, NO. 1, JANUARY 2006, the active current is measured using package resistance and analog-to-digital converters. If the active current measured is greater than a predetermined value, control circuitry in the power measurement circuit reduces the power supplied to the memory chip.
One problem with conventional power measurement circuits and methods is that the leakage measurement circuit does not take into account within die variations in threshold voltage (VT) of transistors or elements in the memory core or between the memory core and the baseline device. In particular, since sub-threshold leakage is exponential dependent on VT variations, performance of a single, internal baseline device is generally not representative of performance of all elements in the memory core, which may contain a million or more memory cells each with one or more active elements.
Another problem with conventional approach is that the circuit and method for measuring power consumption in the active mode is complex increasing the manufacturing and/or operating costs of the circuit or the device in which it is used.
Accordingly, there is a need for an improved power measurement and control circuit and method of operating the same, which are capable of accurately measuring and regulating power by taking into account within die VT variations. It is desirable that the power measurement circuit is capable of operating in both the standby and active power modes. It is further desirable that the power measurement circuit and method achieve these results substantially without increasing circuit complexity and/or manufacturing costs of the circuit or the device in which it is used.
The present invention provides a solution to these and other problems, and offers further advantages over conventional power measurement circuits and methods of operating the same.